Browse Prior Art Database

Automatic Baud Rate and Parity Detection for Asynchronous Communications

IP.com Disclosure Number: IPCOM000122136D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 5 page(s) / 215K

Publishing Venue

IBM

Related People

Novak, TJ: AUTHOR [+3]

Abstract

Described is an algorithm that can be used by one asynchronous station on a point-to-point communications line to detect the baud rate and parity values of another asynchronous station that it wants to communicate with.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 29% of the total text.

Automatic Baud Rate and Parity Detection for Asynchronous Communications

      Described is an algorithm that can be used by one
asynchronous station on a point-to-point communications line to
detect the baud rate and parity values of another asynchronous
station that it wants to communicate with.

      The concept of the invention is to solve the stated problem by
having one station (called the host system) select the values for
baud rate and parity value.  The host system initiates a
communications session by sending a predetermined character sequence
to the other station using the selected values.  The other station
uses this character sequence to determine the values for baud rate
and parity value that the host system has selected.

      The algorithm used to perform the detection is fundamentally
based on the construction of tables as follows:
-  The UART in the receiving station is set to a specific reference
baud rate and parity value.
-  A sending station sends a character from the predetermined
character sequence to the receiving station using a given baud rate
and parity setting.  The output of the receiving station UART (which
is comprised of data characters and status characters) is recorded
and stored in a table.
-  The previous step is repeated for all allowable baud rate and
parity value combinations.  (Sending station UART values are changed.
Receiving station UART remains at the reference rate). The output of
the receiving station UART in each case becomes an entry in a
comparison table.
-  Depending on the range of baud rate values that must be detected,
the reference rate in the receiving station may need to be changed
and more tables built.

      Once completed, the tables constructed in the previous steps
are used by the receiving station to perform the baud rate and parity
detection.  This is accomplished by comparing the output of the UART
with entries in the tables. Once a match is achieved, the baud rate
is known.

      The character sequence transmitted by the host system is
X'55555549', or "UUUI" in ASCII.  The "U"s are used by the attached
station to determine the baud rate and the "I" is used to determine
the parity.  The character "U" was chosen because its binary encoding
(B'01010101') provides a transition at every bit time.  The character
"I" was chosen only because it has the opposite parity of the "U"
character.  Any odd parity character could be used.

      This invention makes the following assumptions:
1.  One of the two stations is designated as the station that will
send the UUUI sequence.  The second station is designated as the
station that will receive the characters and perform the baud rate
and parity detection operation.
2.  The invention assumes no variation in the length of the ASCII
character.  For the attached station, the character length is always
assumed to be 8 bits.  The algorithm can be used unchanged for 7 bit
data.  An extension of the i...